Strip transmission line ferrite filterlimiter having a ferrite sphere positioned beneath overlapping conductors



Nov. 29, 1966 c. E. BROWN 3,289,112

STRIP TRANSMISSION LINE FERRITE FILTER-LIMITER HAVING A FERRITE SPHERE POSITIONED BENEATH OVERLAPFING CONDUGTORS Filed Aug. 31, 1964 Q 5 -INSULAT/ON FIG. 11 6 @W-YIG SPHERE ZNVENTOR. Charles E. Brown ATTORNEY.

United States Patent M STRIP TRANSMISSION LINE FERRITE FILTER- LIMITER HAVING A FETE SPHERE POSI- TIONED BENEATH OVERLAPPING CONDUC- TORS Charles E. Brown, Laurel, Md., assignor to the United States of America as represented by the Secretary of the Navy Filed Aug. 31, 1964, Ser. No. 393,449 3 Claims. (33324.2)

The invention described herein may be manufactured and used by or for the Government of the United States of America. for governmental purposes without the payment of any royalties thereon or therefor.

The present invent-ion relates general-1y to strip transmission line ferrite filter-limiters and more particularly to a ferrite filter-limiter of the above type used as a narrow bandpass filter and power limiter for R.F. signals.

Prior methods o'f ma-kin-g strip transmission line ferrite filter-limiters includethat of cutting a hole in the ground planes of two strip transmission lines and then overlapping the strip transmission lines at right angles to each other so that a yttrium-iron-garnet (YIG) sphere can be inserted in the two holes at the point of overlap. If the point of overlap is an R.F. short circuit and a magnetic field of the proper magnitude is applied to the YIG sphere at right angles to the two transmission lines, filtering and power limiting wil-l occur. For a discussion of the basic principles and theory of operation of ferrimagnetic resonators used as filters in wave guides, strip transmission lines and the like, see P. S. Carter, Jr., Design of Magnetically- Tunable Microwave Filters Using Single Crystal Yttrium- Iron-Garnet Resonators, IRE Trans. on Microwave Theory and Techniques, vol. MTT-9, pp. 2S2-260.

The main disadvantage of the transmission line overlap type of construction is the amount of space required by the two transmission lines and the size of the magnet necessary for applying a field to the YIG sphere. In many applications it is highly desirable to miniaturize these YIG filter structures since a reduction in filter size also means a reduction in magnet size and tuning power requirements.

The present invention is designed to overcome the above disadvantages and to accomplish the objective of miniaturizing these filter strctures. In the present invention only one strip transmission line is used and the center conductors of the strip transmission line are overlapped. The overlapped lines are printed on a pair of opposing dielectric Wal-l members of the strip transmission line. Instead of locating the YIG sphere between the overlapping lines, it is located beneath them in a cavity in one of the dielectric wall members. The two lines are then peeled back and extended through one of the dielectric wall members to a ground plane associated therewith in order to form an R.F. short circuit for signals applied to the center conductors. In this manner the YIG sphere is located beneath the two mutually perpendicular center conductors which form the R.F. short circuit.

Accordingly, it is an object of the present invention to provide a ferrite filter-limiter, the size of which, relative to prior art ferrite filter-limiters, has been greatly reduced.

Another object is to provide a ferrite filter limiter which 3,289,112 Patented Nov. 29, 1966 ermits a reduction in size of the magnet used to establish a DC. field for the YIG resonator.

A further object of the invention is to provide a ferrite filter-limiter having input and output circuits in the same plane.

Other objects and advantages of the present invention will become more fuliy apparent in the following description of the sole embodiment depicted in FIGS. 1 and 2 of the drawing wherein:

FIG. 1 is an exploded view of the strip transmission line ferrite filter-limiter; and

FIG. 2 is a cross-section view of FIG. 1, partly in section, taken in a plane including the longitudinal center line of the ground planes 3 and 8 of FIG. 1.

Referring to FIGS. 1 and 2 there is shown a pair of dielectric wa'll members 10 and 11 having a pair of ground planes 3 and 8 mounted on their outer faces, and a pair of mutually perpendicular center conductors 4 and 6 printed on their inner faces. The center conductors 4 and 6 may be printed on the inner opposing faces of dielectric members 10 and 11 in such a manner that the end portions thereof may be peeled back and bent at right angles to the inner faces of It) and 11 in order that they may be extended through one of the dielectric members 11 to its associated ground plane 8 to make contact therewith and form an R.F. short circuit. The two center conductors 4 and 6 are isolated with a thin film of insulation 5 such as Teflon. The YIG sphere 7 is located beneath the conductors 4 and 6 in a cavity in dielectric member 11 and held in place by a suitable cement. The ground plane 8 has a hole in the center thereof aligned with the cavity in the dielectric wall member 11 in order that the YIG sphere may be inserted in the cavity. The ground plane 8 is made continuous over the cavity with a small sheet of copper 9 and conductive paint. When R.F. signals are applied to conductors 4 and 6 and a DO. biasing field of the proper magnitude is applied to the YIG resonator 7, RF. signals within predetermined frequency ranges will be coupled to the ground planes when the YIG sphere is at or near its point of resonance.

The particular construction of FIGS. 1 and 2 enables the gap of the magnet used to bias the sphere 7 to be reduced by one-half, and a reduction in the gap of the magnet by one-half permits a reduction in the size of the magnet to one-eighth of the conventional size. Since the magnet is by far the largest component in the device, the overall size and weight are greatly reduced.

Another advantage of the invention is that the input and output circuits are in the same plane Where a single strip transmission line is used. This makes the ferrite filter-limiter compatible with other strip transmission line elements.

It should be understood that many design modifications may be made in the embodiment shown in FIGS. 1 and 2 by one skilled in the art without departing from the spirit and scope of the invention. Accordingly, the invention is limited only by way of the following claims.

I claim:

1. A strip transmission line ferrite filter-limiter adapted for use as a narrow bandpass filter and power limiter for RF. signals comprising:

a pair of closely spaced, plane parallel dielectric members having a pair of ground planes mounted on their outer faces and a pair of mutually perpendicular,

overlapping center conductors printed on their inner 3. A strip transmission line ferrite filter-limiter as OPPQSiIIg faces, the nd portions of each of said cOnrecited in claim 2 wherein said ferrite sphere is made of ductors extending perpendicularly from the faces yttriumqmmgamet of said dielectric members through one of said dielectric members to its associated ground plane and 5 References Cited by the Examiner irlalziltkin-g contact therewith to form an R.F. short cir- UNITED STATES PATENTS a ferrite sphere positioned within a cavity in said 0116 3,162,826 12/ 1964 Engelbrecht 33384 dielectric member beneath said overlapping conduc- 3,234,494 2/ 1966 Matthias 333-242 X tors, and 1 7 means for magnetically biasing said ferrite sphere to HERMAN KARL SAALBACH, primary resonance.

2. A strip transmission line ferrite filter-lirniter as re- GENSLER, Assistant Examinercited in claim 1 further comprising a thin film of insulation between said conductors at the point of overlap. 15 

1. A STRIP TRANSMISSION LINE FERRITE FILTER-LIMITER ADAPTED FOR USE AS A NARROW BANDPASS FILTER AND POWER LIMITER FOR R.F. SIGNALS COMPRISING: A PAIR OF CLOSELY SPACED, PLANE PARALLEL DIELECTRIC MEMBERS HAVING A PAIR OF GROUND PLANELS MOUNTED ON THEIR OUTER FACES AND A PAIR OF MUTUALLY PERPENDICULAR, OVERLAPPING CENTER CONDUCTORS PRINTED ON THEIR INNER OPPOSING FACES, THE END PORTIONS OF EACH OF SAID CONDUCTORS EXTENDING PERPENDICULARLY FROM THE FACES OF SAID DIELECTRIC MEMBERS THROUGH ONE OF SAID DIELECTRIC MEMBERS TO ITS ASSOCIATED GROUND PLANE AND MAKING CONTACT THEREWITH TO FORM AN R.F. SHORT CIRCUIT, A FERRITE SPHERE POSITIONED WITHIN A CAVITY IN SAID ONE DIELECTRIC MEMBER BENEATH SAID OVERLAPPING CONDUCTORS, AND MEANS FOR MAGNETICALLY BIASING SAID FERRITE SPHERE TO RESONANCE. 